Print Preview: Disable No Destinations test on Mac

The scenario the test is checking is very uncommon (requires PDF printer
to be disabled, and no printers connected). Flakes are likely related to
the new temporary dom-if added around the user manager. Disable the test
for now, until the timing issue can be resolved or the dom-if can be
removed.

Bug: 1146513
Change-Id: I613557e4fe877e0f4bb2fff5c160a65692cc0eca
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2523248
Commit-Queue: Rebekah Potter <rbpotter@chromium.org>
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Cr-Commit-Position: refs/heads/master@{#825074}

chrome/test/data/webui/print_preview/print_preview_ui_browsertest.js

@@ -1526,9 +1526,16 @@ TEST_F('PrintPreviewDestinationSettingsTest', 'DisabledSaveAsPdf', function() {
   this.runMochaTest(destination_settings_test.TestNames.DisabledSaveAsPdf);
 });
 
-TEST_F('PrintPreviewDestinationSettingsTest', 'NoDestinations', function() {
-  this.runMochaTest(destination_settings_test.TestNames.NoDestinations);
-});
+// Flaky on Mac, see https://crbug.com/1146513.
+GEN('#if defined(OS_MAC)');
+GEN('#define MAYBE_NoDestinations DISABLED_NoDestinations');
+GEN('#else');
+GEN('#define MAYBE_NoDestinations NoDestinations');
+GEN('#endif');
+TEST_F(
+    'PrintPreviewDestinationSettingsTest', 'MAYBE_NoDestinations', function() {
+      this.runMochaTest(destination_settings_test.TestNames.NoDestinations);
+    });
 
 GEN('#if defined(OS_CHROMEOS)');
 // eslint-disable-next-line no-var